KR102374928B1 - Wireless communication terminal and wireless communication method for random access-based uplink multi-user transmission - Google Patents

Abstract

The present invention relates to a wireless communication terminal and a wireless communication method for uplink multi-user transmission based on random access, and more particularly, to a wireless communication terminal and a wireless communication method for efficiently performing contention for random access in an uplink multi-user transmission process. is about
To this end, the present invention provides a wireless communication terminal, comprising: a processor; and a communication unit, wherein the processor obtains a backoff counter for uplink multi-user random access of the terminal, wherein the backoff counter is obtained within a contention window for uplink multi-user random access, and When a trigger frame indicating user transmission is received, and the trigger frame indicates at least one resource unit allocated for random access, the resource unit(s) in which random access can be performed in response to the trigger frame decrement the backoff counter based on the number, select at least one of the resource unit(s) allocated for the random access when the backoff counter is 0 or decremented to 0, and increase it through the selected resource unit A wireless communication terminal for performing multi-user transmission and a wireless communication method using the same are provided.

Description

Wireless communication terminal and wireless communication method for random access-based uplink multi-user transmission

The present invention relates to a wireless communication terminal and a wireless communication method for uplink multi-user transmission based on random access, and more particularly, to a wireless communication terminal and a wireless communication method for efficiently performing contention for random access in an uplink multi-user transmission process. is about

Recently, with the spread of mobile devices, a wireless LAN technology that can provide fast wireless Internet services to them has been in the spotlight. Wireless LAN technology is a technology that allows mobile devices such as smart phones, smart pads, laptop computers, portable multimedia players, and embedded devices to wirelessly access the Internet in a home, business, or specific service area based on wireless communication technology in a short distance. am.

Since IEEE (Institute of Electrical and Electronics Engineers) 802.11 supported an initial wireless LAN technology using a 2.4 GHz frequency, standards for various technologies are being commercialized or developed. First, IEEE 802.11b supports a communication speed of up to 11 Mbps while using a frequency of the 2.4 GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses a frequency of 5 GHz band instead of 2.4 GHz band, thereby reducing the influence on interference compared to a fairly crowded 2.4 GHz band frequency, and using OFDM technology to maximize communication speed Up to 54 Mbps. However, IEEE 802.11a has a disadvantage in that the communication distance is shorter than that of IEEE 802.11b. And, like IEEE 802.11b, IEEE 802.11g uses a frequency of the 2.4 GHz band to achieve a communication speed of up to 54 Mbps and has received considerable attention as it satisfies backward compatibility. have the upper hand

In addition, IEEE 802.11n is a technical standard established to overcome the limitation on communication speed, which has been pointed out as a weakness in wireless LAN. IEEE 802.11n aims to increase the speed and reliability of the network and extend the operating distance of the wireless network. More specifically, IEEE 802.11n supports high throughput (HT) with a data processing rate of up to 540 Mbps or higher, and uses multiple antennas at both ends of the transmitter and receiver to minimize transmission errors and optimize data rates. It is based on MIMO (Multiple Inputs and Multiple Outputs) technology. In addition, this standard may use a coding method that transmits multiple duplicate copies to increase data reliability.

As the spread of wireless LAN is activated and applications using it are diversified, the need for a new wireless LAN system to support a very high throughput (VHT) higher than the data processing speed supported by IEEE 802.11n has emerged. became Among them, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at 5GHz frequency. The IEEE 802.11ac standard is defined only in the 5GHz band, but for backward compatibility with existing 2.4GHz band products, the initial 11ac chipsets will also support operation in the 2.4GHz band. Theoretically, according to this standard, the wireless LAN speed of multiple stations is at least 1 Gbps, and the maximum single link speed is at least 500 Mbps. This is achieved by extending the air interface concepts adopted by 802.11n, including wider radio frequency bandwidths (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256 QAM). In addition, there is IEEE 802.11ad as a method of transmitting data using a 60GHz band instead of the existing 2.4GHz/5GHz. IEEE 802.11ad is a transmission standard that provides a speed of up to 7 Gbps using beamforming technology, and is suitable for high-bit-rate video streaming such as large-capacity data or uncompressed HD video. However, the 60 GHz frequency band has a disadvantage in that it is difficult to pass through obstacles and can only be used between devices in a short distance.

Meanwhile, in recent years, as a next-generation wireless LAN standard after 802.11ac and 802.11ad, discussions are continuing to provide high-efficiency and high-performance wireless LAN communication technology in a high-density environment. That is, in the next-generation wireless LAN environment, high-frequency-efficiency communication must be provided indoors and outdoors in the presence of high-density stations and access points (APs), and various technologies are required to implement it.

As described above, an object of the present invention is to provide high-efficiency/high-performance wireless LAN communication in a high-density environment.

In addition, an object of the present invention is to efficiently manage a random access process of a plurality of terminals.

In order to solve the above problems, the present invention provides a wireless communication terminal and a wireless communication method of the following terminal.

First, according to an embodiment of the present invention, there is provided a wireless communication terminal comprising: a processor; and a communication unit, wherein the processor obtains a backoff counter for uplink multi-user random access of the terminal, wherein the backoff counter is obtained within a contention window for uplink multi-user random access, and When a trigger frame indicating user transmission is received, and the trigger frame indicates at least one resource unit allocated for random access, the resource unit(s) in which random access can be performed in response to the trigger frame decrement the backoff counter based on the number, select at least one of the resource unit(s) allocated for the random access when the backoff counter is 0 or decremented to 0, and increase it through the selected resource unit A wireless communication terminal for performing multi-user transmission is provided.

Also according to an embodiment of the present invention, there is provided a wireless communication method for a wireless communication terminal, comprising: obtaining a backoff counter for uplink multi-user random access of the terminal, wherein the backoff counter is a contention window for uplink multi-user random access obtained within the scope of; Receiving a trigger frame indicating uplink multi-user transmission; When the trigger frame indicates at least one resource unit allocated for random access, decreasing the backoff counter based on the number of resource unit(s) on which random access can be performed in response to the trigger frame step; and when the backoff counter is 0 or decremented to 0, performing uplink multi-user transmission through a resource unit selected from among the resource unit(s) allocated for the random access. .

The processor, when carrier sensing is required before uplink multi-user transmission corresponding to the trigger frame, performs carrier sensing of a channel including the selected resource unit, and as a result of the carrier sensing, the channel including the selected resource unit is If it is determined as an idle state, uplink multi-user data is transmitted through the selected resource unit.

The processor, when it is determined that the channel including the selected resource unit is in an occupied state as a result of the carrier sensing, does not transmit uplink multi-user data through the selected resource unit, but does not transmit uplink multi-user data through the selected resource unit within the contention window range. A new backoff counter for user random access is randomly obtained, and the new backoff counter is used to participate in the next upstream multi-user random access.

The contention window for acquiring the new backoff counter has the same size as the existing contention window.

The carrier sensing is performed during the SIFS time between the trigger frame and a PHY protocol data unit (PPDU) transmitted in response to the trigger frame.

The processor decrements the backoff counter when there is pending data to be transmitted to the base wireless communication terminal.

The contention window minimum value and contention window maximum value for determining the contention window are transmitted through a random access parameter set.

The set of random access parameters is included in beacon and probe responses.

The uplink multi-user random access is an uplink OFDMA-based random access.

According to an embodiment of the present invention, it is possible to efficiently manage the random access process of a plurality of terminals.

According to an embodiment of the present invention, it is possible to reduce the probability of collision occurrence by preventing excessive accumulation of terminals having a backoff counter of 0 for random access.

According to an embodiment of the present invention, it is possible to increase the overall resource usage rate and improve the performance of the WLAN system in the contention-based channel access system.

1 shows a wireless LAN system according to an embodiment of the present invention.
2 illustrates a wireless LAN system according to another embodiment of the present invention.
3 shows the configuration of a station according to an embodiment of the present invention.
4 shows a configuration of an access point according to an embodiment of the present invention.
5 schematically illustrates a process in which an STA establishes a link with an AP.
6 illustrates a Carrier Sense Multiple Access (CSMA)/Collision Avoidance (CA) method used in wireless LAN communication.
7 illustrates an embodiment of an operation of an uplink transmission terminal in an uplink multi-user transmission process.
8 illustrates an embodiment of a subsequent operation of an uplink transmission terminal when uplink multi-user transmission fails.
9 illustrates another embodiment of a subsequent operation of an uplink transmission terminal when uplink multi-user transmission fails.
10 illustrates another embodiment of a subsequent operation of an uplink transmission terminal when uplink multi-user transmission fails.
11 shows an embodiment of a UL OFDMA-based random access procedure.
12 to 15 show embodiments of a UL OFDMA-based random access procedure when carrier sensing is required before transmission of a trigger-based PPDU.
16 to 18 show embodiments of an OBO counter management method of an STA that has succeeded in UL OFDMA-based random access.
19 and 20 show embodiments of a UL OFDMA-based random access procedure when the STA has no pending data to be transmitted.
21 and 22 illustrate protection methods of a UL OFDMA-based random access procedure.

The terms used in the present specification have been selected as widely used general terms as possible while considering their functions in the present invention, but these may vary depending on intentions, conventions, or emergence of new technologies of those of ordinary skill in the art. In addition, in certain cases, there are terms arbitrarily selected by the applicant, and in this case, the meaning will be described in the description of the relevant invention. Therefore, it is intended to clarify that the terms used in this specification should be interpreted based on the actual meaning of the terms and the contents of the entire specification, rather than the names of simple terms.

Throughout the specification, when a component is said to be “connected” with another component, this includes not only “directly connected” but also “electrically connected” with other components in between. do. In addition, when a certain component "includes" a specific component, this means that other components may be further included, rather than excluding other components, unless otherwise stated. In addition, the limitation of “greater than” or “less than” based on a specific threshold value may be appropriately replaced with “greater than” or “less than”, respectively, depending on the embodiment.

This application claims priority on the basis of Korean Patent Application Nos. 10-2016-0057759, 10-2016-0117898 and 10-2017-0002720, Examples and descriptions are intended to be included in the detailed description of the present application.

1 illustrates a wireless LAN system according to an embodiment of the present invention. The WLAN system includes one or more basic service sets (BSS), which indicate a set of devices that can communicate with each other by successfully synchronizing. In general, the BSS can be divided into an infrastructure BSS (infrastructure BSS) and an independent BSS (IBSS), and FIG. 1 shows the infrastructure BSS among them.

As shown in FIG. 1 , the infrastructure BSS (BSS1, BSS2) includes one or more stations (STA1, STA2, STA3, STA4, STA5), an access point (PCP/AP) that is a station providing a distribution service. -1, PCP/AP-2), and a Distribution System (DS) connecting a plurality of access points (PCP/AP-1, PCP/AP-2).

A station (Station, STA) is an arbitrary device that includes a medium access control (MAC) and a physical layer interface to a wireless medium that comply with the provisions of the IEEE 802.11 standard, and in a broad sense, a non-access point ( Includes both non-AP stations as well as access points (APs). Also, in this specification, the term 'terminal' may be used to indicate a non-AP STA, an AP, or both. The station for wireless communication includes a processor and a communication unit, and may further include a user interface unit and a display unit according to an embodiment. The processor may generate a frame to be transmitted through the wireless network or process a frame received through the wireless network, and may perform various other processes for controlling the station. In addition, the communication unit is functionally connected to the processor and transmits and receives frames through a wireless network for the station. In the present invention, a terminal may be used as a term including a user equipment (UE).

An access point (AP) is an entity that provides access to a distribution system (DS) via a wireless medium for a station associated with it. In the infrastructure BSS, in principle, communication between non-AP stations is performed via the AP, but when a direct link is established, direct communication is also possible between non-AP stations. Meanwhile, in the present invention, the AP is used as a concept including a Personal BSS Coordination Point (PCP), and broadly speaking, a centralized controller, a base station (BS), a Node-B, a BTS (Base Transceiver System), or a site. It may include all concepts such as a controller. In the present invention, the AP may also be referred to as a base wireless communication terminal, and the base wireless communication terminal is a term including all of an AP, a base station, an eNB (eNodeB), and a transmission point (TP) in a broad sense. can be used as In addition, the base wireless communication terminal may include various types of wireless communication terminals for allocating a communication medium resource and performing scheduling in communication with a plurality of wireless communication terminals.

A plurality of infrastructure BSSs may be interconnected through a distribution system (DS). In this case, a plurality of BSSs connected through the distribution system are referred to as extended service sets (ESSs).

2 illustrates an independent BSS as a wireless LAN system according to another embodiment of the present invention. In the embodiment of Fig. 2, the same or corresponding parts to the embodiment of Fig. 1 will be omitted redundant description.

Since BSS3 shown in FIG. 2 is an independent BSS and does not include an AP, all stations STA6 and STA7 are not connected to the AP. The independent BSS is not allowed to access the distribution system and forms a self-contained network. In the independent BSS, each of the stations STA6 and STA7 may be directly connected to each other.

3 is a block diagram showing the configuration of a station 100 according to an embodiment of the present invention. As shown, the station 100 according to an embodiment of the present invention may include a processor 110 , a communication unit 120 , a user interface unit 140 , a display unit 150 , and a memory 160 .

First, the communication unit 120 transmits and receives wireless signals such as wireless LAN packets, and may be built-in or externally provided in the station 100 . According to an embodiment, the communication unit 120 may include at least one communication module using different frequency bands. For example, the communication unit 120 may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 may include a communication module using a frequency band of 6 GHz or higher and a communication module using a frequency band of 6 GHz or lower. Each communication module may perform wireless communication with an AP or an external station according to a wireless LAN standard of a frequency band supported by the corresponding communication module. The communication unit 120 may operate only one communication module at a time or a plurality of communication modules simultaneously according to the performance and requirements of the station 100 . When the station 100 includes a plurality of communication modules, each communication module may be provided in an independent form, or a plurality of modules may be integrated into one chip. In an embodiment of the present invention, the communication unit 120 may represent an RF communication module that processes a radio frequency (RF) signal.

Next, the user interface unit 140 includes various types of input/output means provided in the station 100 . That is, the user interface unit 140 may receive a user input using various input means, and the processor 110 may control the station 100 based on the received user input. In addition, the user interface unit 140 may perform an output based on a command of the processor 110 using various output means.

Next, the display unit 150 outputs an image on the display screen. The display unit 150 may output various display objects such as content executed by the processor 110 or a user interface based on a control command of the processor 110 . In addition, the memory 160 stores a control program used in the station 100 and various data corresponding thereto. The control program may include an access program necessary for the station 100 to access an AP or an external station.

The processor 110 of the present invention may execute various commands or programs and process data inside the station 100 . In addition, the processor 110 may control each unit of the above-described station 100 , and may control data transmission/reception between the units. According to an embodiment of the present invention, the processor 110 may execute a program for accessing the AP stored in the memory 160 and receive a communication setting message transmitted by the AP. Also, the processor 110 may read information on the priority condition of the station 100 included in the communication setup message, and request access to the AP based on the information on the priority condition of the station 100 . The processor 110 of the present invention may refer to the main control unit of the station 100, and may refer to a control unit for individually controlling some components of the station 100, such as the communication unit 120, according to an embodiment. may be That is, the processor 110 may be a modem or a modulator and/or demodulator that modulates and demodulates a radio signal transmitted and received from the communication unit 120 . The processor 110 controls various operations of wireless signal transmission and reception of the station 100 according to an embodiment of the present invention. Specific examples thereof will be described later.

The station 100 shown in FIG. 3 is a block diagram according to an embodiment of the present invention, and the separated blocks are logically divided into device elements. Accordingly, the elements of the above-described device may be mounted as one chip or a plurality of chips according to the design of the device. For example, the processor 110 and the communication unit 120 may be integrated into one chip or implemented as a separate chip. In addition, in an embodiment of the present invention, some components of the station 100 , such as the user interface unit 140 and the display unit 150 , may be selectively provided in the station 100 .

4 is a block diagram showing the configuration of the AP 200 according to an embodiment of the present invention. As shown, the AP 200 according to an embodiment of the present invention may include a processor 210 , a communication unit 220 , and a memory 260 . In FIG. 4 , redundant descriptions of parts identical to or corresponding to those of the station 100 of FIG. 3 among the configuration of the AP 200 will be omitted.

Referring to FIG. 4 , the AP 200 according to the present invention includes a communication unit 220 for operating the BSS in at least one frequency band. As described above in the embodiment of FIG. 3 , the communication unit 220 of the AP 200 may also include a plurality of communication modules using different frequency bands. That is, the AP 200 according to an embodiment of the present invention may include two or more communication modules in different frequency bands, for example, 2.4 GHz, 5 GHz, and 60 GHz. Preferably, the AP 200 may include a communication module using a frequency band of 6 GHz or higher and a communication module using a frequency band of 6 GHz or less. Each communication module may perform wireless communication with a station according to a wireless LAN standard of a frequency band supported by the communication module. The communication unit 220 may operate only one communication module at a time or a plurality of communication modules simultaneously according to the performance and requirements of the AP 200 . In an embodiment of the present invention, the communication unit 220 may represent an RF communication module that processes a radio frequency (RF) signal.

Next, the memory 260 stores a control program used in the AP 200 and various data corresponding thereto. The control program may include an access program for managing access of stations. In addition, the processor 210 may control each unit of the AP 200 , and may control data transmission/reception between the units. According to an embodiment of the present invention, the processor 210 may execute a program for connection with a station stored in the memory 260 and transmit a communication setting message for one or more stations. In this case, the communication setting message may include information on the access priority condition of each station. In addition, the processor 210 performs connection establishment according to the connection request of the station. According to an embodiment, the processor 210 may be a modem or a modulator and/or demodulator that modulates and demodulates a radio signal transmitted and received from the communication unit 220 . The processor 210 controls various operations of wireless signal transmission and reception of the AP 200 according to an embodiment of the present invention. Specific examples thereof will be described later.

5 schematically illustrates a process in which an STA establishes a link with an AP.

Referring to FIG. 5 , the link between the STA 100 and the AP 200 is largely established through three steps of scanning, authentication, and association. First, the scanning step is a step in which the STA 100 acquires access information of the BSS operated by the AP 200 . As a method for performing scanning, a passive scanning method in which information is obtained using only a beacon message S101 periodically transmitted by the AP 200, and a probe request by the STA 100 to the AP There is an active scanning method for transmitting a probe request (S103) and receiving a probe response from the AP (S105) to obtain access information.

The STA 100 successfully receiving the radio access information in the scanning step transmits an authentication request (S107a), receives an authentication response from the AP 200 (S107b), and performs the authentication step do. After the authentication step is performed, the STA 100 transmits an association request (S109a) and receives an association response from the AP 200 (S109b) to perform the association step. In the present specification, association basically means wireless coupling, but the present invention is not limited thereto, and coupling in a broad sense may include both wireless coupling and wired coupling.

Meanwhile, an additional 802.1X-based authentication step (S111) and an IP address acquisition step (S113) through DHCP may be performed. In FIG. 5 , the authentication server 300 is a server that processes 802.1X-based authentication with the STA 100 , and may exist physically coupled to the AP 200 or exist as a separate server.

6 illustrates a Carrier Sense Multiple Access (CSMA)/Collision Avoidance (CA) method used in wireless LAN communication.

A terminal performing wireless LAN communication checks whether a channel is busy by performing carrier sensing before transmitting data. If a radio signal of a predetermined strength or higher is detected, it is determined that the corresponding channel is busy, and the terminal delays access to the corresponding channel. This process is called clear channel assessment (CCA), and the level at which a corresponding signal is detected is called a CCA threshold. If a radio signal greater than the CCA threshold value received by the terminal has the corresponding terminal as a receiver, the terminal processes the received radio signal. On the other hand, when no radio signal is detected in the corresponding channel or when a radio signal having an intensity smaller than the CCA threshold is detected, it is determined that the channel is in an idle state.

When it is determined that the channel is in the idle state, each terminal having data to transmit performs a backoff procedure after a time in Inter Frame Space (IFS), such as AIFS (Arbitration IFS), PIFS (PCF IFS), etc. according to the situation of each terminal. do. According to an embodiment, the AIFS may be used as a configuration to replace the existing DIFS (DCF IFS). Each terminal waits while decrementing the slot time as much as the random number determined by the terminal, that is, the backoff counter during the interval of the channel's idle state, and the terminal that has exhausted all the slot times attempts access to the corresponding channel will do In this way, a period in which each terminal performs a backoff procedure is referred to as a contention window period.

If a specific terminal successfully accesses the channel, the corresponding terminal may transmit data through the channel. However, when a terminal attempting access collides with another terminal, the collided terminals are each assigned a new random number (ie, a backoff counter) and perform the backoff procedure again. According to an embodiment, the random number newly allocated to each terminal may be determined within a range (2*CW) twice the range of random numbers previously used by the corresponding terminal (contention window, CW). On the other hand, each terminal attempts to access by performing the backoff procedure again in the next contention window period, and in this case, each terminal performs the backoff procedure from the remaining slot time in the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid collision with each other for a specific channel.

Multi-user transfer

When OFDMA (Orthogonal Frequency Division Multiple Access) or Multi Input Multi Output (MIMO) is used, one wireless communication terminal may transmit data to a plurality of wireless communication terminals simultaneously. In addition, a plurality of wireless communication terminals may transmit data to one wireless communication terminal at the same time. For example, downlink multi-user (DL-MU) transmission in which the AP simultaneously transmits data to a plurality of STAs, and uplink multi-user in which a plurality of STAs simultaneously transmit data to the AP (Uplink Multi-User) , UL-MU) transmission may be performed.

In order to perform UL-MU transmission, a resource unit to be used by each STA performing uplink transmission and a transmission start time should be determined. According to an embodiment of the present invention, the UL-MU transmission process may be managed by the AP. UL-MU transmission may be performed in response to a trigger frame transmitted by the AP. The trigger frame indicates UL-MU transmission after the SIFS time of a PHY protocol data unit (PPDU) carrying the trigger frame. In addition, the trigger frame carries resource unit allocation information for the UL-MU transmission. When the AP transmits a trigger frame, a plurality of STAs transmit uplink data through each allocated resource unit at a time point designated by the trigger frame. UL-MU transmission corresponding to the trigger frame is performed through a trigger-based PPDU. After the uplink data transmission is completed, the AP transmits ACKs to STAs that have successfully transmitted uplink data. In this case, the AP may transmit a preset multi-STA block ACK (Multi-STA Block ACK, M-BA) as an ACK for a plurality of STAs.

In a non-legacy WLAN system, a specific number, for example, 26, 52, or 106 tones, may be used as a resource unit for subchannel access in a channel of a 20 MHz band. Accordingly, the trigger frame may indicate identification information of each STA participating in UL-MU transmission and information of an allocated resource unit. The identification information of the STA includes at least one of an association ID (AID), partial AID, and MAC address of the STA. In addition, the resource unit information includes size and location information of the resource unit.

7 illustrates an embodiment of an operation of an uplink transmission terminal in an uplink multi-user transmission process. As described above, STAs participating in UL-MU transmission are allocated a resource unit through the trigger frame 310, and receive an Aggregate MAC Protocol Data Unit (MPDU) or an Aggregate MPDU (A-MPDU) through the allocated resource unit. send. In this case, the STA configures and transmits the (A-)MPDU 320 according to the transmission length specified in the trigger frame 310 .

An STA participating in UL-MU transmission may configure an (A-)MPDU 320 based on information in an Enhanced Distributed Channel Access (EDCA) buffer of the corresponding UE at the time of receiving the trigger frame 310 . More specifically, the STA considers the backoff counter and the AIFSN value remaining for each access category in the EDCA buffer, and determines the priority among the access categories at the channel access time of the UL-MU transmission. The (A-)MPDU 320 to be transmitted by the STA may first be composed of data of the determined highest priority access category. Next, the (A-)MPDU 320 may be configured to include data of an access category of the next priority within the allowed transmission length of the STA. Referring to FIG. 7 , the priority between access categories in the EDCA buffer of STA1 participating in UL-MU transmission is determined in the order of VI (video), VO (voice), BK (background), and BE (best effort). . Accordingly, STA1 configures the (A-)MPDU 320 with data of the highest priority VI access category. In addition, the STA1 may fill the remaining length within the allowed transmission length of the (A-)MPDU 320 with data of the VO and BK categories of the next priority.

According to an embodiment of the present invention, if the STA transmits a buffer status report (BSR) to the AP before the trigger frame 310 is transmitted, and the target traffic of the BSR still remains in the EDCA buffer, the STA sends the corresponding traffic (A-)MPDU can be configured with the highest priority. If the allowed transmission length of the STA remains, the STA may configure the remaining part of the (A-)MPDU based on the priority among the aforementioned access categories.

8 illustrates an embodiment of a subsequent operation of an uplink transmission terminal when uplink multi-user transmission fails. In the contention-based channel access process, each terminal uses and manages a backoff counter as in the embodiment of FIG. 6 for single-user transmission. However, when participating in trigger-based UL-MU transmission, the STA may perform UL-MU transmission regardless of the backoff counter managed by the STA. When the STA succeeds in UL-MU transmission, the STA may initialize a backoff counter and a retry counter. If there is subsequent data in the queue of the same access category, the STA may participate in channel contention by allocating a new backoff counter for the subsequent data.

However, when the UL-MU transmission of the STA fails, the STA may resume the transmission process for the corresponding data. According to an embodiment of the present invention, when a response corresponding to the trigger-based PPDU transmitted by the STA is not received, it may be determined that the UL-MU transmission by the STA has failed. The STA may transmit data that has failed to be transmitted in the UL-MU transmission process through the next UL-MU transmission process or the single user transmission process of the corresponding STA. According to the embodiment of FIG. 8 , when data that has failed to be transmitted in the UL-MU transmission process is transmitted through the single-user transmission process of the corresponding STA, the STA performs channel access using the existing backoff counter for single-user transmission. can do. The existing backoff counter for single-user transmission is a backoff counter maintained by the STA before the corresponding UL-MU transmission process. That is, when UL-MU transmission fails, the STA may attempt channel access by reusing the backoff counter maintained for single-user transmission.

More specifically, FIG. 8 illustrates a process in which STA1, in which UL-MU transmission has failed, retryes data transmission through single-user transmission. In FIG. 8 and the following drawings, x and y in <x, y> indicate the remaining backoff counter and retry counter of the corresponding terminal. Before receiving the trigger frame for the UL-MU transmission process, the remaining backoff counter of STA1 was 3. STA1 transmits a trigger-based PPDU in the UL-MU transmission process, but does not receive a response corresponding thereto. Accordingly, STA1 may retry transmission of the corresponding data through a single user transmission process. In this case, STA1 may attempt channel access for single-user transmission using the remaining backoff counter 3 . When the backoff counter expires in a subsequent backoff procedure, STA1 may perform single-user transmission.

9 illustrates another embodiment of a subsequent operation of an uplink transmission terminal when uplink multi-user transmission fails. As in the embodiment of FIG. 8 , when the STA, which has failed in UL-MU transmission, retryes data transmission using the existing backoff counter for single-user transmission, the STA transmits the same data twice or more through one contention. you may have a chance In this case, the fairness of channel access between the STA participating in the UL-MU transmission and the STA not participating in the UL-MU transmission is misaligned.

Therefore, according to another embodiment of the present invention, the STA in which UL-MU transmission has failed considers that single-user transmission has failed and performs the next channel access procedure. To this end, an STA participating in UL-MU transmission may decrease the backoff counter maintained by the STA to 0. If the UL-MU transmission fails, the STA increments the retry counter for the corresponding access category by 1 and acquires a new backoff counter in the contention window range based on the increased retry counter. As the retry counter increases, the contention window of the STA may be changed from the first contention window to the second contention window. When the size of the first contention window is not the maximum size of the contention window, the size of the second contention window may be a value obtained by adding 1 to twice the size of the first contention window. The STA acquires a new backoff counter within the second contention window, and performs channel access using the acquired new backoff counter.

Referring to FIG. 9 , the size of the first contention window of STA1 is 15, and channel access is performed using the backoff counter 7 obtained within the first contention window. In the first backoff procedure, the backoff counter of STA1 is decreased to 3, and the UL-MU transmission process by the trigger frame is started. STA1 participating in the UL-MU transmission process may decrement the backoff counter to 0 and attempt to transmit a trigger-based PPDU. However, as the UL-MU transmission of STA1 fails, STA1 retries transmission of the corresponding data through single-user transmission. STA1 increments the retry counter for the corresponding access category by 1, and acquires a new backoff counter 13 within the size 32 of the second contention window based on the incremented retry counter. STA1 performs channel access using the acquired new backoff counter 13.

Meanwhile, when carrier sensing is required before transmission of the trigger-based PPDU, the STA may not transmit the trigger-based PPDU because the channel is determined to be occupied as a result of the carrier sensing. According to an additional embodiment of the present invention, when the trigger-based PPDU is not transmitted because the channel is determined to be occupied as a result of carrier sensing, the UL-MU transmission by the STA may not be considered as failed. Accordingly, the STA may not increment the retry counter for single-user transmission.

10 illustrates another embodiment of a subsequent operation of an uplink transmission terminal when uplink multi-user transmission fails. When participating in UL-MU transmission corresponding to the trigger frame received from the AP, the STA should attempt data transmission at an unintended timing. Therefore, according to another embodiment of the present invention, a penalty due to UL-MU transmission failure can be reduced. More specifically, when the UL-MU transmission fails, the STA acquires a new backoff counter in the existing contention window range without increasing the retry counter. The STA performs channel access using the acquired new backoff counter.

Referring to FIG. 10 , the size of the initial contention window of STA1 is 15, and channel access is performed using the backoff counter 7 obtained within the initial contention window. In the first backoff procedure, the backoff counter of STA1 is decreased to 3, and the UL-MU transmission process by the trigger frame is started. STA1 participating in the UL-MU transmission process may decrement the backoff counter to 0 and attempt to transmit a trigger-based PPDU. However, as the UL-MU transmission of STA1 fails, STA1 retries transmission of the corresponding data through single-user transmission. STA1 acquires a new backoff counter 8 within the size 15 of the existing contention window. STA1 performs channel access using the acquired new backoff counter 8.

Upward multi-user random access

In a non-legacy WLAN system, UL-MU random access may be performed. In an embodiment of the present invention, UL-MU random access may be performed through UL OFDMA-based random access. However, the present invention is not limited thereto. When the trigger frame transmitted by the AP indicates resource unit(s) allocated for random access, STAs may perform random access through the resource unit(s). A resource unit (ie, random resource unit) for random access may be identified through a preset AID value. When the AID subfield of the user information field in the trigger frame indicates a preset AID value, a resource unit corresponding thereto may be identified as a random resource unit. STAs may select at least one of random resource unit(s) indicated through the trigger frame and attempt UL-MU transmission through the selected random resource unit.

STAs attempting UL OFDMA-based random access compete to obtain a transmission opportunity. A separate OFDMA backoff (OBO) counter is used for contention in UL OFDMA based random access. The OBO counter is obtained within the range of the OFDMA contention window (OCW) managed for each STA. The AP transmits the OCW minimum value (ie, OCWmin) and the OCW maximum value (ie, OCWmax) for each STA's OCW determination through a random access parameter set. The random access parameter set may be transmitted while being included in at least one of a beacon, a probe response, a (re)association response, and an authentication response. The STA that first attempts UL OFDMA-based random access sets the OCW of the STA to 'OCWmin - 1' based on the received random access parameter set. Then, the STA acquires an OBO counter by selecting a random integer in the range from 0 to OCW. In an embodiment of the present invention, the OBO counter and the OCW may indicate a backoff counter for UL-MU random access and a contention window for UL-MU random access, respectively.

STAs decrement their OBO counters by the number of resource unit(s) on which random access can be performed, whenever every trigger frame is transmitted. That is, when N resource unit(s) are allocated to random access, STAs may decrease the OBO counter by up to N in random access contention in the UL-MU transmission process by the corresponding trigger frame. According to an embodiment of the present invention, the STA may decrement the OBO counter when it has pending data to be transmitted to the AP. If the OBO counter of the STA is less than or equal to the number of resource unit(s) on which random access can be performed, the OBO counter of the STA is decremented to zero. If the OBO counter is 0 or is decreased to 0, the STA may randomly select at least one of the resource unit(s) allocated for random access, and may perform UL-MU transmission through the selected resource unit. An STA that fails to decrease the OBO counter to 0 in the corresponding contention process may attempt random access by repeating the above-described OBO counter decrement process when the next trigger frame is transmitted.

11 illustrates an embodiment of a UL OFDMA-based random access procedure. Each STA performs contention for UL OFDMA-based random access using an OBO counter. In the embodiment of Figure 11, the trigger frame 312 indicates four random resource units. STAs that have received the trigger frame 312 decrement the OBO counter of the STA based on the number of random resource units 4 . At this time, the OBO counters of STA1, STA2, and STA4 having OBO counters less than or equal to 4 in the number of random resource units are decreased to 0. Accordingly, STA1 , STA2 , and STA4 may transmit a trigger-based PPDU by selecting one of the random resource units allocated by the trigger frame 312 .

In the embodiment of FIG. 11 , STA1 and STA4 select the same random resource unit and transmit a trigger-based PPDU, which causes collision. Accordingly, STA1 and STA4 do not receive a response corresponding to the transmitted trigger-based PPDU. When the UL OFDMA-based random access fails, the STA increases the OCW at a preset rate and randomly acquires a new OBO counter within the increased OCW range. As the OCW increases, the OCW of the STA may be changed from the first OCW to the second OCW. If the size of the first OCW is not the maximum OCW value, the size of the second OCW may be a value obtained by adding 1 to twice the size of the first OCW. However, if the size of the existing OCW of the STA is equal to the maximum OCW value, the STA does not increase the OCW even if random access fails. That is, if the size of the first OCW is equal to the maximum OCW value, the second OCW may be set equal to the first OCW. 11 , STA1 and STA4 may randomly acquire a new OBO counter in the increased second OCW, respectively, and use the acquired new OBO counter to participate in the following UL OFDMA-based random access process.

12 to 15 illustrate embodiments of a UL OFDMA-based random access procedure when carrier sensing is required before transmission of a trigger-based PPDU. In the embodiments of each drawing, redundant descriptions of parts identical to or corresponding to the embodiments of the previous drawings will be omitted.

12 illustrates a first embodiment of a UL OFDMA-based random access procedure when carrier sensing is required before transmission of a trigger-based PPDU. When carrier sensing is required before transmission of the trigger-based PPDUs 422 and 522, STAs must perform carrier sensing for a channel to be accessed. The trigger frames 412 and 512 may indicate whether carrier sensing before transmission of the trigger-based PPDUs 422 and 522 is required through a separate 'CS required' field. In this case, the carrier sensing may be performed during the SIFS time between the trigger frames 412 and 512 and the trigger-based PPDUs 422 and 522 transmitted corresponding thereto.

As described above, STAs whose OBO counter is 0 or decreased to 0 may attempt random access by selecting one of the random resource units. In this case, the STA performs carrier sensing of a channel including the selected resource unit. When the channel including the selected resource unit is determined to be in an idle state as a result of carrier sensing, the STA may transmit a trigger-based PPDU through the selected resource unit. However, when it is determined that the channel including the selected resource unit is in the occupied state as a result of carrier sensing, the STA cannot transmit the trigger-based PPDU through the selected resource unit. When the trigger-based PPDU is not transmitted because the channel is determined to be occupied as a result of the carrier sensing, OCW and OBO counters for the STA to participate in the next UL OFDMA-based random access procedure must be determined.

According to the first embodiment of the present invention, when the trigger-based PPDU is not transmitted because the channel is determined to be occupied as a result of the carrier sensing, the STA maintains the OBO counter at the time and participates in the next UL OFDMA-based random access process. can That is, the STA maintains the OBO counter at 0 and participates in the following UL OFDMA-based random access process. If carrier sensing is required before transmission of the trigger-based PPDU even in the following UL OFDMA-based random access procedure, the STA may transmit the trigger-based PPDU when it is determined that the channel including the selected resource unit is in an idle state.

Referring to FIG. 12 , the first trigger frame 412 indicates 5 random resource units, and sets the 'CS required' field to 1 to request carrier sensing before transmission of the trigger-based PPDU. STAs that have received the first trigger frame 412 decrement the OBO counter of the STA based on the number of random resource units 5. In this case, the OBO counters of STA1, STA2, and STA4 having OBO counters equal to or less than 5 in the number of random resource units are decreased to 0. STA1, STA2, and STA4 perform carrier sensing for channel access. The channel sensed by STA1 was determined to be in the idle state, but the channels sensed by STA2 and STA4 were determined to be in the occupied state. Accordingly, STA1 transmits a trigger-based PPDU 422 in response to the first trigger frame 412 , but STA2 and STA4 do not perform random access. In this case, STA2 and STA4 may suspend random access and participate in the following UL OFDMA-based random access process while maintaining OBO counter 0.

12, the second trigger frame 512 indicates 5 random resource units, and sets the 'CS required' field to 1 to request carrier sensing before transmission of the trigger-based PPDU. STAs that have received the second trigger frame 512 decrement the OBO counter of the STA based on the number of random resource units 5. In this case, the OBO counters of STA3, STA5, and STA7 having an OBO counter equal to or less than 5 in the number of random resource units are decreased to 0. In addition, OBO counters of STA2 and STA4 for which random access is reserved in the previous UL OFDMA-based random access process are 0. Accordingly, STA2, STA4, STA3, STA5, and STA7 perform carrier sensing for channel access. Channels sensed by STA2 and STA 7 were determined to be idle, but channels sensed by STA4, STA3, and STA5 were determined to be occupied. Accordingly, STA2 and STA7 transmit a trigger-based PPDU 522 in response to the second trigger frame 512 , but STA4 , STA3 and STA5 do not perform random access.

13 illustrates a second embodiment of a UL OFDMA-based random access procedure when carrier sensing is required before transmission of a trigger-based PPDU. When STAs having an OBO counter of 0 are accumulated in a continuous UL OFDMA-based random access process, the probability of collision of random access STAs within a limited resource unit increases. Therefore, according to the second embodiment of the present invention, when the trigger-based PPDU is not transmitted because the channel is determined to be occupied as a result of carrier sensing, the STA acquires a new OBO counter and participates in the following UL OFDMA-based random access process. More specifically, the STA randomly acquires a new OBO counter in the existing OCW, and participates in the following UL OFDMA-based random access process using the acquired new OBO counter. If the STA does not access the channel due to the carrier sensing result, it cannot be regarded as a transmission failure, and the channel for random access is not affected. Accordingly, the OCW for acquiring the new OBO counter may have the same size as the existing OCW.

Referring to FIG. 13 , the first trigger frame 414 indicates 5 random resource units, and sets the 'CS required' field to 1 to request carrier sensing before transmission of the trigger-based PPDU. 12 , STA1 , STA2 , and STA4 whose OBO counter is decreased to 0 among STAs receiving the first trigger frame 414 perform carrier sensing for channel access. The channel sensed by STA1 was determined to be in the idle state, but the channels sensed by STA2 and STA4 were determined to be in the occupied state. Accordingly, STA1 transmits a trigger-based PPDU 424 in response to the first trigger frame 414 , but STA2 and STA4 do not perform random access. STA2 and STA4 may suspend random access, acquire a new OBO counter, and participate in the following UL OFDMA-based random access process. In this case, the new OBO counters of STA2 and STA4 may be acquired in the existing OCW of the corresponding STA, respectively. In the embodiment of FIG. 13 , STA2 acquires a new OBO counter 7 and STA4 acquires a new OBO counter 5 .

In the embodiment of FIG. 13 , the second trigger frame 514 indicates five random resource units, and sets the 'CS required' field to 1 to request carrier sensing before transmission of the trigger-based PPDU. Among the STAs that have received the second trigger frame 514 , STA3, STA4, STA5, and STA7 whose OBO counter is reduced to 0 perform carrier sensing for channel access. Channels sensed by STA3 and STA 7 were determined to be idle, but channels sensed by STA4 and STA5 were determined to be occupied. Accordingly, STA3 and STA7 transmit a trigger-based PPDU 524 in response to the second trigger frame 514 , but STA4 and STA5 do not perform random access. On the other hand, the new OBO counter 7 obtained by STA2 is greater than the number of random resource units 5 indicated by the second trigger frame 514 . Accordingly, STA2 also does not transmit the trigger-based PPDU, and may participate in the following UL OFDMA-based random access procedure using the remaining backoff counter 2 .

14 illustrates a third embodiment of a UL OFDMA-based random access procedure when carrier sensing is required before transmission of a trigger-based PPDU. As described above, when STAs having an OBO counter of 0 are accumulated in a continuous UL OFDMA-based random access process, the probability of collision of random access STAs within a limited resource unit increases. According to the third embodiment of the present invention, when the trigger-based PPDU is not transmitted because the channel is determined to be occupied as a result of carrier sensing, it may be considered that the UL OFDMA-based random access has failed. Accordingly, the STA increases the OCW at a preset rate and randomly acquires a new OBO counter within the increased OCW range. As in the above-described embodiment, the increased size of the OCW may be a value obtained by adding 1 to twice the size of the existing OCW. The STA randomly acquires a new OBO counter within the increased OCW range and participates in the following UL OFDMA-based random access process.

Referring to FIG. 14 , the transmission process of the first trigger frame 416 and the trigger-based PPDU 426 corresponding thereto is as described in the embodiments of FIGS. 12 and 13 . As a result of the carrier sensing, STA2 and STA4 determined as the channel occupied state do not perform random access. STA2 and STA4 may suspend random access, acquire a new OBO counter, and participate in the following UL OFDMA-based random access process. In this case, the new OBO counters of STA2 and STA4 may be acquired within the increased OCW of the corresponding STA, respectively. In the embodiment of FIG. 14 , STA2 acquires a new OBO counter 7 and STA4 acquires a new OBO counter 5 . After STA2 and STA4 each acquire a new OBO counter, the transmission process of the second trigger frame 516 and the corresponding trigger-based PPDU 526 is as described in the embodiment of FIG. 13 .

15 illustrates a fourth embodiment of a UL OFDMA-based random access procedure when carrier sensing is required before transmission of a trigger-based PPDU. According to the fourth embodiment of the present invention, when carrier sensing is required before transmission of the trigger-based PPDU, the STA may determine whether to decrease the OBO counter according to the carrier sensing result. When it is determined that the channel including the selected resource unit is in the idle state as a result of carrier sensing, the STA may perform the above-described OBO counter reduction process. However, when it is determined that the channel including the selected resource unit is in the occupied state as a result of carrier sensing, the STA may participate in the following UL OFDMA-based random access process while maintaining the OBO counter without decreasing the OBO counter. Through this, it is possible to prevent STAs having an OBO counter of 0 from being accumulated in a continuous UL OFDMA-based random access process.

Referring to FIG. 15 , the first trigger frame 418 indicates 5 random resource units, and sets the 'CS required' field to 1 to request carrier sensing before transmission of the trigger-based PPDU. STAs that have received the first trigger frame 418 perform carrier sensing before transmission of the trigger-based PPDU. Channels sensed by STA1, STA4, and STA5 were determined to be idle, but channels sensed by STA2 and STA3 were determined to be occupied. Accordingly, STA1, STA4, and STA5 decrement the OBO counter in response to the first trigger frame 418, but STA2 and STA3 do not decrement the OBO counter. In this case, STA2 and STA3 may suspend random access and participate in the following UL OFDMA-based random access process while maintaining a corresponding OBO counter. Similarly, the STAs that have received the second trigger frame 518 perform carrier sensing before transmission of the trigger-based PPDU. STA3 and STA5 determined to be occupied by the channel on which the carrier sensing has been performed do not decrease the OBO counter in response to the second trigger frame 518 .

The AP may allocate multiple channels for random access. According to an embodiment of the present invention, STAs may determine whether to decrease the OBO counter by performing carrier sensing for all channels. However, according to another embodiment of the present invention, STAs may perform carrier sensing for each allocated 20 MHz channel. In this case, the STAs may attempt random access only to the random resource unit included in the channel determined to be in the idle state. According to an embodiment of the present invention, the STA may decrease the OBO counter based on the number of random resource unit(s) included in the channel determined to be idle.

16 to 18 illustrate embodiments of a method for managing an OBO counter of an STA that has succeeded in UL OFDMA-based random access.

As described above, the AP may transmit the random access parameter set to the STAs through the beacon 600 or the like. The random access parameter set includes an OCW minimum value and an OCW maximum value for each STA's OCW determination, or information capable of deriving the values. STAs attempting UL OFDMA-based random access determine an OCW between an OCW minimum value and an OCW maximum value, and randomly select an OBO counter within the OCW range. When the trigger frames 610 and 620 transmitted by the AP indicate at least one random resource unit (or when one or more user information fields having a preset AID value indicating random access exist), the STAs are Random access may be attempted through at least one of the random resource unit(s).

If the UL OFDMA-based random access fails, the STA increases the OCW and randomly acquires a new OBO counter within the increased OCW range. As in the above-described embodiment, the increased size of the OCW may be a value obtained by adding 1 to twice the size of the existing OCW. The STA randomly acquires a new OBO counter within the increased OCW range and participates in the following UL OFDMA-based random access process. On the other hand, when the UL OFDMA-based random access is successful, the STA resets the OCW to the OCW minimum value. In this case, a rule is required for an STA that has succeeded in UL OFDMA-based random access to acquire a new OBO counter.

First, according to the embodiment of FIG. 16 , an STA that has succeeded in UL OFDMA-based random access may participate in the following UL OFDMA-based random access process while maintaining the existing OBO counter. That is, the STA maintains the OBO counter at 0 and participates in the following UL OFDMA-based random access process. Referring to FIG. 16 , the first trigger frame 610 indicates four random resource units, and the second trigger frame 620 indicates two random resource units. Upon receiving the first trigger frame 610, the OBO counter of STA1 is decremented to 0, and STA1 succeeds in transmitting the trigger-based PPDU. STA1, which has succeeded in UL OFDMA-based random access, resets the OCW to the minimum OCW value and maintains the OBO counter at 0. When receiving the second trigger frame 620, the OBO counter of STA1 is 0, so STA1 may transmit a trigger-based PPDU again. As such, if the OBO counter is maintained at 0, the STA continues to obtain a random access opportunity until the UL OFDMA-based random access fails.

17 is another embodiment of the present invention, an STA that has succeeded in UL OFDMA-based random access may acquire a new OBO counter based on the reset OCW. In this case, the size of the reset OCW may be the same as the minimum OCW value. The STA participates in the following UL OFDMA-based random access process using the new OBO counter. Referring to FIG. 17 , the OBO counter of STA1 that has received the first trigger frame 610 is decremented to 0, and STA1 succeeds in transmitting the trigger-based PPDU. STA1, which has succeeded in UL OFDMA-based random access, resets the OCW to the OCW minimum value, and acquires a new OBO counter 5 within the reset OCW. STA1 participates in the following UL OFDMA-based random access process using the new OBO counter 5. Upon receiving the second trigger frame 620, the OBO counter of STA1 is decreased to 3, and since the OBO counter is not decreased to 0, STA1 does not perform random access. STA1 participates in the following UL OFDMA-based random access process using the remaining OBO counter 3.

18 illustrates another embodiment of the present invention, an STA that has succeeded in UL OFDMA-based random access may not participate in random access until it receives a new random access parameter set. In the embodiment of FIG. 18 , the STA1 that has succeeded in random access in response to the first trigger frame 610 does not perform additional UL OFDMA-based random access until the next beacon 700 including the random access parameter set is received. Accordingly, STA1 does not perform separate random access when the second trigger frame 620 is received. According to an embodiment, the STA1 may not reset the OCW and OBO counters until receiving a new random access parameter set.

19 illustrates an embodiment of a UL OFDMA-based random access procedure when the STA does not have pending data to be transmitted. The STA instructed to transmit the trigger-based PPDU may not transmit data or transmit one or more QoS Null frames when there is no pending uplink data. However, if the STA without pending uplink data transmits the QoS Null frame even in the random access process, the probability of collision in the random resource unit increases. Accordingly, according to an embodiment of the present invention, the STA can participate in the UL OFDMA-based random access procedure only when it has pending data to be transmitted to the AP. An STA that has no pending data to be transmitted does not transmit any data including a QoS Null frame through random access.

20 illustrates another embodiment of a UL OFDMA-based random access procedure when the STA does not have pending data to be transmitted. According to another embodiment of the present invention, when an STA having no data to be transmitted in the EDCA buffer receives a trigger frame indicating a random resource unit, whether to attempt random access may be determined according to the selection of the STA.

As shown in FIG. 20A , STA1 participating in random access to transmit information such as a buffer status report may perform the above-described OBO counter decrement process. When the OBO counter is decreased to 0, the STA1 may randomly select at least one of the random resource unit(s) to transmit a QoS Null frame. STA1 that has succeeded in UL OFDMA-based random access may reset OCW and acquire a new OBO counter.

However, as shown in FIG. 20(b) , when STA1 does not transmit even a QoS Null frame, STA1 does not perform an OBO counter decrement process. That is, according to an embodiment of the present invention, the STA may decrement the OBO counter only when it has pending data to be transmitted to the AP. Since STA1 does not participate in the random access, it does not reset the OCW after the corresponding random access process. That is, STA1 participates in the following UL OFDMA-based random access process using the existing OCW and OBO counters.

21 and 22 illustrate protection methods of a UL OFDMA-based random access procedure. Multi-user RTS (MU-RTS) may be used to protect data transmission in the multi-user transmission process. The MU-RTS may have a modified format of the trigger frame, and may induce simultaneous CTS transmission of at least one receiver through the user information field. Recipients receiving MU-RTS transmit simultaneous CTS after SIFS time. Simultaneous CTS transmitted by multiple receivers have the same waveform. Neighboring terminals that have received the MU-RTS and/or the simultaneous CTS may configure a Network Allocation Vector (NAV).

According to an embodiment of the present invention, it is possible to protect the UL OFDMA-based random access process through the transmission of the MU-RTS and the simultaneous CTS. However, in the random access process, it is not possible to determine in advance which STA will attempt random access for data transmission. If all STAs attempting random access transmit the CTS at the same time, unnecessary protection may be performed not only for the STA that succeeds in the actual random access but also the radio range of the STA that fails the random access. As a result, performance degradation of the adjacent network may occur. Accordingly, there is a need for a method for minimizing the number of STAs that transmit simultaneous CTSs among STAs that will perform random access.

21 illustrates an embodiment of a method of protecting a UL OFDMA-based random access procedure. According to an embodiment of the present invention, the AP may transmit information on the number of random resource unit(s) to be used in the UL OFDMA-based random access process by inserting into the MU-RTS. An STA attempting random access extracts information on the number of random resource units from the received MU-RTS. The STA determines whether the OBO counter of the STA can be decremented to 0 in the subsequent UL OFDMA-based random access process with reference to the extracted information on the number of random resource units. If the OBO counter can be decremented to 0, the STA transmits a simultaneous CTS. However, if the OBO counter cannot be decremented to 0, the STA does not transmit a simultaneous CTS.

Referring to FIG. 21 , the number of random resource units to be used in the UL OFMDA-based random access process is 4. The AP transmits information on the number of the random resource units through the MU-RTS. STAs that have received the MU-RTS acquire information on the number of random resource units, and determine whether the OBO counter of the corresponding STA can be decremented to 0 with reference to the obtained information. In this case, STA1, STA2, and STA3 having an OBO counter less than or equal to 4, which is the number of random resource units, simultaneously transmit CTS. However, STA4 and STA5 having an OBO counter greater than 4, which is the number of random resource units, cannot reduce the OBO counter to 0 in the subsequent UL OFDMA-based random access process, and thus do not transmit the simultaneous CTS.

According to an embodiment of the present invention, the MU-RTS may indicate information on the number of random resource unit(s) to be used in a UL OFDMA-based random access procedure following various methods. According to an embodiment, the MU-RTS may indicate a separately designated identifier for random access through the AID field or the 'type-dependent per user info' field, and repeat this by the number of random resource unit(s). According to another embodiment, the MU-RTS may indicate a separately designated identifier for random access through the AID field, and may indicate information on the number of random resource unit(s) through a 'type-dependent per user info' field. According to another embodiment of the present invention, an identifier that can represent the number of random resource unit(s) may be designated and inserted into the AID field of the 'per user info' field of the MU-RTS. According to another embodiment of the present invention, the MU-RTS may include a separate identifier indicating random access, and may indicate information on the number of random resource unit(s) through a specific resource unit pattern in the resource unit allocation field. .

22 illustrates another embodiment of a method of protecting a UL OFDMA-based random access procedure. When UL-MU transmission is performed a plurality of times within the same TXOP, MU-RTS and CTS transmission/reception to target STAs in the entire UL-MU transmission process may be performed at once at the beginning of the TXOP. In this case, the AP may transmit information on the total number of random resource unit(s) to be used in UL OFDMA-based random access procedures that are to be protected by inserting into the MU-RTS. The MU-RTS may indicate information on the total number of random resource unit(s) to be used in subsequent UL OFDMA-based random access procedures through at least one of the methods described in FIG. 21 .

Referring to FIG. 22 , two UL OFMDA-based random access procedures are performed within the same TXOP, and the total number of random resource units to be used in these processes is 9. The AP transmits information on the total number of the random resource units through the MU-RTS. STAs that have received the MU-RTS acquire information on the total number of random resource units, and determine whether the OBO counter of the corresponding STA can be decremented to 0 with reference to the acquired information. STA1 to STA5 all have OBO counters less than or equal to 9, and therefore, the corresponding STAs can transmit CTS simultaneously.

As described above, the present invention has been described using wireless LAN communication as an example, but the present invention is not limited thereto and may be equally applied to other communication systems such as cellular communication. Further, although the methods, apparatuses, and systems of the present invention have been described with reference to specific embodiments, some or all of the components, operations, and/or components of the present invention may be implemented using a computer system having a general-purpose hardware architecture.

The above-described embodiments of the present invention may be implemented through various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.

In the case of implementation by hardware, the method according to embodiments of the present invention may include one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), and Programmable Logic Devices (PLDs). , FPGAs (Field Programmable Gate Arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, the method according to the embodiments of the present invention may be implemented in the form of a module, procedure, or function that performs the functions or operations described above. The software code may be stored in the memory and driven by the processor. The memory may be located inside or outside the processor, and data may be exchanged with the processor by various known means.

The above description of the present invention is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, the embodiments described above are exemplary in all respects and should be construed as being limited. For example, each component described as a single type may be implemented in a dispersed form, and likewise components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims rather than the above detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention. do.

Although various embodiments of the present invention have been described with a focus on the IEEE 802.11 system, they may be applied to other various types of mobile communication devices, mobile communication systems, and the like.

Claims (20)

A wireless communication terminal comprising:
processor; and
including a communication department;
The processor is
Receiving contention window information related to a contention window for performing an uplink orthogonal frequency division multiple access (OFDMA)-based random access (UORA) of the terminal,
The contention window information includes a minimum value of the contention window,
The contention window is set based on the minimum value,
Selecting an OFDMA random access backoff (OBO) counter within the range of the contention window,
Receive a trigger frame including resource allocation information,
When the value of the OBO counter is less than the number of one or more resource units allocated based on the resource allocation information, the OBO counter is set to '0'.
The method of claim 1,
The initial value of the contention window is set to the minimum value.
The method of claim 1, wherein the processor comprises:
selecting a resource unit from among the one or more resource units;
When a specific field included in the trigger frame indicates to perform carrier sensing, performing carrier sensing in a channel including the selected resource unit,
The OBO counter is decremented by the number of the one or more resource units.
4. The method of claim 3,
The channel including the resource unit selected for uplink multi-user transmission in response to the trigger frame among the one or more resource units is busy according to the carrier sensing, and the OBO counter is '0'' or '0', a new OBO counter is determined within the contention window before the next trigger frame is received.
5. The method of claim 4, wherein the processor comprises:
Participate in a subsequent UORA (subsequent UORA) using the new OBO counter,
When the channel is determined to be busy based on the carrier sensing, the uplink multi-user transmission is not performed through the selected resource unit,
The new OBO counter is arbitrarily determined within the range of the contention window.
6. The method of claim 5,
The contention window for determining the new OBO counter has the same size as the existing contention window.
5. The method of claim 4,
When the channel including the resource unit is idle according to the carrier sensing and the OBO counter is decremented to '0' or '0', the uplink multi-user transmission is based on the selected resource unit. A wireless communication terminal performed.
4. The method of claim 3,
The carrier sensing is performed during the SIFS time between the trigger frame and a PHY protocol data unit (PPDU) transmitted in response to the trigger frame.
The method of claim 1,
When the trigger frame is received and there is no pending data to be transmitted to the base wireless communication terminal, the OBO counter is not decremented.
The method of claim 1,
The minimum value of the contention window is transmitted through a random access parameter set.
A wireless communication method of a wireless communication terminal, comprising:
Receiving contention window information related to a contention window for performing an uplink orthogonal frequency division multiple access (OFDMA)-based random access (UORA) of the terminal ,
The contention window information includes a minimum value of the contention window,
the contention window is set based on the minimum value; and
selecting an OFDMA random access backoff (OBO) counter within the contention window;
Receive a trigger frame including resource allocation information,
When the value of the OBO counter is less than the number of one or more resource units allocated based on the resource allocation information, the OBO counter is set to '0'.
12. The method of claim 11,
The initial value of the contention window is set to the minimum value.
12. The method of claim 11,
selecting a resource unit from among the one or more resource units; and
When a specific field included in the trigger frame indicates to perform carrier sensing, the method further comprising: performing carrier sensing on a channel including the selected resource unit;
The OBO counter is decremented by the number of the one or more resource units.
14. The method of claim 13,
The channel including the resource unit selected for uplink multi-user transmission in response to the trigger frame among the one or more resource units is busy according to the carrier sensing, and the OBO counter is '0'' or '0', a new OBO counter is determined within the contention window before the next trigger frame is received.
15. The method of claim 14,
The method further comprising the step of participating in a subsequent UORA (subsequent UORA) using the new OBO counter,
When the channel is determined to be busy based on the carrier sensing, the uplink multi-user transmission is not performed through the selected resource unit,
The new OBO counter is arbitrarily determined within the range of the contention window.
16. The method of claim 15,
The contention window for determining the new OBO counter has the same size as an existing contention window.
15. The method of claim 14,
When the channel including the resource unit is idle according to the carrier sensing and the OBO counter is decremented to '0' or '0', the uplink multi-user transmission is based on the selected resource unit. A method of wireless communication performed.
14. The method of claim 13,
The carrier sensing is a wireless communication method performed during the SIFS time between the trigger frame and a PHY protocol data unit (PPDU) transmitted in response to the trigger frame.
12. The method of claim 11,
When the trigger frame is received and there is no pending data to be transmitted to the base wireless communication terminal, the OBO counter is not decremented.
12. The method of claim 11,
The minimum value of the contention window is transmitted through a random access parameter set.

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